This invention relates to a vehicle used for transporting freight loads, commonly referred to as a semi-trailer.
For purposes of highway shipment, unit loads of wall board, lumber and the like are routinely placed on a flatbed semi-trailer which in turn is attached to, and supported by a fifth wheel device on a modern truck tractor.
Currently semi-trailers of the type referred to are primarily constructed of longitudinal and transverse steel support members, attached to and covered by heavy gauge sheet metal flooring or decking sections, resulting in a platform like upper surface upon which the unit loads of freight are loaded.
Normally semi-trailers are loaded by utilizing standard motorized forklift trucks. This loading procedure requires dunnage to be placed between the underside of each unit freight load and the flatbed semi-trailer upper surface, as well as between each subsequent layer of freight. This dunnage allows for space in which the forklike projections of a forklift truck can be maneuvered during loading and unloading operations, as well as providing support for the unit freight loads during transport.
The result of the above-described standard semi-trailer construction, combined with the significant amounts of dunnage normally required to properly load a standard 40 foot semi-trailer with freight, is a highway vehicle normally having an overall weight in excess of 15 tons, not including the weight of the commodity to be transported.
The fuel expense associated with the operation of such a semi-trailer/truck tractor in addition to the state and federal restrictions on highway vehicle weight have long since created need for a practical transport vehicle designed to allocate only the minimum amount of weight necessary to the actual vehicle structure itself and any dunnage required, thus allowing for a maximum amount of freight capacity.
One prior attempt at overall weight reduction design suggested dividing the standard 40 foot length of a semi-trailer into two equal sections, joined together and supported by another series of wheels at the 20 foot point. This design reduced the load requirements of the individual support members and therefore allowed for the use of lighter weight support beams. However, maneuverability of this design proved problematical and positioning the freight to achieve proper weight distribution made loading procedures difficult and time consuming.